The present invention relates to a rotating electrical machine control system, a vehicle drive system and a temperature estimation method
There exists a rotating electrical machine control system that limits the torque of a rotating electrical machine based on the temperature of a coolant that cools an inverter device (which is an example of an inverter in the present invention) in Japanese Patent Application Publication No. JP-A-2005-86848.
JP-A-2005-86848 relates to, for example, an electric automobile including a motor as a drive source, in which a control device for the inverter device includes a cooling medium temperature detection unit that detects the coolant temperature and a torque limit unit that limits an output torque of the motor when a vehicle comes to a stalled state. The torque limit unit limits the output torque based on the coolant temperature.
In JP-A-2005-86848, since the torque limitation is performed in accordance with the coolant temperature, a switching element can be protected more effectively in accordance with the state of a cooling unit compared to a configuration in which the temperature of a particular portion of the inverter device is simply detected to execute the torque limitation.
Nowadays, in relation to environmental issues, hybrid vehicles that include both an engine and a rotating electrical machine as drive sources and which drive while appropriately selecting and determining the operation states of both drive sources in accordance with the driving state are attracting attention.
Japanese Patent Application Publication No. JP-A-2006-149064 shows a rotating electrical machine control system provided in such hybrid vehicles. A vehicle described in JP-A-2006-149064 includes an engine and a pair of motors as drive sources. In the technology disclosed in JP-A-2006-149064 as well, a cooling device that cools an inverter device is provided, and the load rate of a rotating electrical machine drive system is reduced in accordance with the fluctuation in cooling performance of the cooling device. Specifically, current flowing in an inverter is reduced (to consequently perform the torque limitation described above).
The rotating electrical machine drive system disclosed in Japanese Patent Application Publication No. JP-A-2006-149064 includes a DC power supply, a voltage conversion portion, and an inverter (as an example of a frequency conversion portion in the present invention) for executing a DC-to-AC conversion. The voltage conversion portion increases the power supply voltage, and the inverter performs conversion to an AC current and supplies the AC current of a predetermined current value to the motor at a predetermined frequency. Thus, the motor rotates at a rotational speed in accordance with the frequency of the supplied current, and generates a torque in accordance with the current value. In the rotating electrical machine control system provided in the hybrid vehicle including the voltage conversion portion, the voltage (which is called an inverter voltage in the present invention and is also the voltage applied to the motor) applied to the frequency conversion portion may reach as high as about twice a battery voltage after the voltage increase.